(Adds quotes from Petkovic's lawyer)
Jan 4 (Reuters) - Vladimir Petkovic has been sacked as coach of Lazio and replaced by his predecessor Edoardo Reja, the club confirmed in a statement on Saturday.
Petkovic, who signed a deal just before Christmas to take charge of the Swiss national side from next season, contested the decision via his lawyer who described it as "unfair and illegitimate."
Reja, 68, had taken charge of training sessions this week even though Petkovic had said that he been told nothing in writing by Lazio and still considered himself to be their coach.
Even though Petkovic will not begin his new role until after his contract with Lazio has expired in June, club president Claudio Lotito was still reported by Italian media to be angry over the move.
"Lazio communicates that it has terminated the employment contract with Vladimir Petkovic for just cause following the conclusion of a disciplinary procedure and (after hearing the) justification of the interested parties," said the club in a statement.
Petkovic's lawyer Paco D'Onofrio said Lazio had failed to state which rule Petkovic had supposedly violated.
"We consider the statement to be unfair and illegitimate because no rule has been broken at any point," he told Sky Sports Italia in a telephone interview. "The Lazio statement itself does not mention which rule he has violated.
"No rule forbids a coach from reaching an agreement with any other party when his contract is due to expire. Indeed, Petkovic signed for a national team and not a club rival of Lazio."
Switzerland announced on Dec. 23 that Petkovic had agreed replace Ottmar Hitzfeld who will leave after the World Cup in Brazil.
The Bosnia-born coach led Lazio to seventh place in Serie A last season plus the Coppa Italia title with a win over neighbours AS Roma in the final.
This season has been less impressive and they are 10th in the table with 20 points from 17 games and Petkovic's future had been the subject of speculation before the Swiss announcement.
Reja has coached around 20 clubs since starting his career in 1980, including Napoli, Genoa, Torino and Cagliari. He was previously in charge at Lazio for two years before he resigned and was replaced by Petkovic following the 2011/12 season.
Reja's first game in charge will be at home to Inter Milan on Monday. Lazio are the fifth Serie A side to change coach this season following Catania, Sampdoria, Genoa and Chievo. (Reporting by Brian Homewood, editing by Pritha Sarkar)